The present disclosure relates to a method for operating a wind turbine, in particular a method for operating a wind turbine, the wind turbine including a wind rotor having at least one rotor blade and a generator connected to the wind rotor, wherein the generator is adapted to be connected to a grid. Further, the present disclosure relates to a wind turbine. In particular the present disclosure relates to a wind turbine, the wind turbine including a wind rotor having at least one rotor blade and a generator connected to the wind rotor, wherein the generator is adapted to be connected to a grid.
When starting a wind turbine, typically, the wind rotor is arrested by a parking brake. Then, the wind speed is measured. The rotor blades are moved into the wind by a blade pitch system when the wind speed is within the operating range of the wind turbine, for example 6 to 24 m/s. In a typical embodiment, the wind turbine is started if the wind speed exceeds a predetermined speed, for example 3.5 m/s. Then, the wind turbine is operated in a spinning mode. In the spinning mode, a spinning rotation of a wind rotor or a rotor of a generator is measured and an average of the spinning rotation is calculated. When the wind turbine is rotating in the spinning rotation, a blade pitch is about 60 degrees with respect to the plane of rotation. In the event that this calculated average exceeds a predetermined value of the rotational speed of the wind rotor, the turbine runs up. In the run-up procedure, the blade pitch angle is modified to an operating pitch angle between −1 to 20 degrees with respect to the plane of rotation. After the run-up procedure, the wind turbine is idling for cut-in and the generator of the wind turbine is connected to the grid. Typically, the wind turbine is operated, such that the rotational speed of the wind rotor is controlled and held substantially constant for a predetermined time, for example more than 25 seconds, at a predetermined rotational speed, such that the rotational speed of the wind turbine may be synchronized with the grid and subsequently connected with the grid. Thus, the wind turbine goes into the state of a load or partial load operation. Then, the wind turbine accelerates further to the optimal operation point.
Typically, wind turbines are controlled by a programmable logic circuit (PLC). The software running on the PLC controls the behavior of the turbine dependent on sensors, actors, external connected devices, the actual wind turbine state, etc. Typically, a state machine may control the run up of the wind turbine. This state machine includes typically a “cut-in” state in which the generator speed is controlled to a cut-in speed. For example, the turbine goes online if the actual generator speed reaches and stays at the cut-in speed. A speed control, for example a closed loop control, regulates the generator speed to this cut-in speed. The speed control is typically realized by controlling the pitch of the blades.